Engine ignition system cable



July 17, 1962 E; 1. SHOBERT N ENGINE IGNITION SYSTEM CABLE Filed Dec. l2, 1960 INVEN TOR. feaf. Hoef/2r JZ BY uw/ amfmwmd A 7' 7' ORNE K5 casting channels.

3,045,199 ENGINE IGNITION SYSTEM CABLE Erle I. Shobert II, St. Marys, Pa., assigner to Stackpole Carbon Company, St. Marys, Pa., a corporation of Pennsylvania Filed Dec. 12, 1960. Ser. No. 75,324 4 Claims. (Cl. 338-66) This invention relates to ignition cables, such as connect a distributor With the spark plugs of an internal combustion engine, and more particularly to cables that reduce interference by an engine with television reception.

The ignition systems of vehicles produce electromagnetic radiations in the frequency range of television broad- Such radiations therefore interfere with nearby television reception. Two methods of su'- pressing objectionable radiations have been proposed, but neither is satisfactory. When a resistor is placed at each end of an ignition cable containing a solid metal conductor, the impulses from the spark at each end of the system are reduced, but the cable is still shock excited throughout its length and can radiate with very little damping, at a frequency determined by its inductance and its capacity to ground. It has also been proposed to use an ignition cable in which the entire flexible cable is an electric resistor. This is accomplished by molding a mixture of carbon particles and la suitable plastic, such as rubber. Theoretically, such a cable should be effective, but in actual practice the normal flexing and vibration of the cable causes arcing to occur in the cable so that the resistance of the cable changes. Furthermore, many people object to using resistance cables because it is so ditlicult to make suitable connections to their ends. This is because the distributed carbon resistance inside the insulating material must be engaged by the metal terminals, and the reliability of such contact cannot be depended upon unless the connection is made under factory condi tions.

It is among the objects of this invention to provide an electric resistance cable, in which there will be no arcing or change of resistance, in which the resistance value can readily be controlled, which can be checked easily for electrical `breaks or failures, and to which electric terminals can be secured easily and depeudably.

In accordance with this invent-ion a plurali-ty of longitudinally spaced rigid resistors have flexible wire leads extending from their opposite ends and electrically connecting them together in series. The resistors and the Wires between them are completely enclosed by a flexible insulating sheath molded around them. The Wire leads are of such length that the ends of the sheath can be stripped back to expose the end wires sothat they can be connected to terminals without exposing the end resistors.

The preferred embodiment of the invention is illustrated in the accompanying drawings, in which FIG. 1 is a central longitudinal section of my ignition cable;

FIG. 2 is a similar view of a length of the cable, With the central portion in elevation, showing metal terminals mounted on the ends; and

FIG. 3 is an enlarged cross section of the cable taken on the line III- III of FIG. 1.

Referring to FIG. l of the drawings, a flexible string of xed resistors 1 is l`formed by connecting a number of them end' to end by llexible wire leads 2,-all of which have substantially the same length. Each resistor may be a rigid cylindrical element molded from a mixture of an insulating plastic and carbon or graphite particles in a Well known manner. The leads project from both ends of each resistor, in which they are embedded.

The string of resistors is insulated and protected by a flexible sheath 3 of any suitable insulating material, such nited States Patent O 3,045,199 Patented July 17, 1962 as rubber. 'This material is molded or extruded around the resistors and their connecting wires. The cable thus formed can be made in any length and coiled on a reel, from which shorter ignition cables of any desired length can be cut. The long cable can be cut between any pair `of adjacent resistors because the hard lumps formed by them can easily be felt.

The resistance of the individual resistors is determined by their size, the spacing they are to have in an ignition cable, and the total resistance desired for the cable. There can be considerable variation in the resistance of the cable without adversely affecting its use in an ignition system, because the total resistance of an ignition cable in use is always small in comparison with the resistance of the spark gap at the spark plug to which the cable is connected. Since it is desired to have the electrical resistance distributed along the cable as uniformly as possible, the resistors should be short enough to permit them to be located close together. On the other hand, they must be spaced sufficiently far apart to permit the use of connecting wires that will still be long enough, after any wire is cut in half, to permit the end wires thus formed to be stripped of insulation suiiiciently for engagement by metal terminals, but without exposing the end resistors. Accordingly, the connecting wire leads should not be less than about an inch long between resistors, but to avoid spacing the resistors too far apart, the wires should not be more than about four inches long.

When the cable is cut about midway between a pair of resistors to form a short ignition cable and the insulating sheath of the latter has been stripped back to expose the end wires, end connect-ions can be made in exactly the same way as they would be if a stand-ard conductor cable had been used. Thus, as shown in IFIG. 2, a distributor terminal 4 and a spark plug terminal 5 can be crimped on the opposite ends of the cable in tight contact with the exposed ends of the end wires bent over the ends of the sheath. Unlike a standard cable, however, this new ignition cable has the advantages of one containing a distributed resistance, because the fixed resistors are distributed along its length.

An ignition cable made in accordance with this invention will cause little, if any, interference witht'elevision reception and yet it will perform its primary function as well as a standard conductor. Unlike a cable in which electrical resistance is produced by iinely divided carbon or graphite distributed throughout its length, with my cable there is no problem in making connections to its ends because there are Wire leads that can be engaged by the terminals mounted on the cable. Obviously, the resistors are not affected by tlexing of the cable or by its vibration in use.

According to the provisions of the patent statutes, I have explained the principle of my 4invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it under stood that, Within the scope of the appended claims, the invention may lbe practiced otherwise than as specifically illustrated and described.

I claim:

1. An engine ignition `system electric resistance cable comprising a single prefabricated string of longitudinally spaced rigid resistors, flexible Wire leads extending from both ends of every resistor and electrically connecting them in series, and a flexible imperforate insulating sheath completely enclosing the resistors and the leads between them, the leads and sheath being concentric and the leads being of such length that the end-s of the sheath can be stripped back to expose the end leads sufficiently for connection to terminals without exposing the end resistors.

2. An electric resistance cable according to claim l, in which the wire leads between the resistors are all of substantially uniform length between about one inch and four inches long.

3. An engine ignition system electric resistance cable comprising a single prefabr-icatedstring of rigid resistors and exible Wire leads having ends embedded lin both ends of every resistor and electrically connecting them in series, a flexible imperforate insulating sheath completely enclosing the resistors and the leads between them, the leads and sheath being concentric and the leads being of `such `length that the end leads project from the ends of the sheath covering the outer ends of the end resistors, and metal terminals secured to the ends of the sheath in engagement with the projecting ends of said end leads.

4. The method of making electric resistance cables for an engine ignition system, comprising embedding the opposite ends of a plurality of wire leads in the opposite ends of a series of longitudinally spaced resistors to form a string of resistors, enclosing said string in the center of an insulating sheath, and severing said sheath land Wires substantially midway between adjacent resistors at intervals along said string to form short length ignition cables.

References Cited` in the tile of this patent UNITED STATES PATENTS 2,792,481 Wood May 14, 1957 

